linux/drivers/char/raw.c
Tejun Heo e525fd89d3 block: make blkdev_get/put() handle exclusive access
Over time, block layer has accumulated a set of APIs dealing with bdev
open, close, claim and release.

* blkdev_get/put() are the primary open and close functions.

* bd_claim/release() deal with exclusive open.

* open/close_bdev_exclusive() are combination of open and claim and
  the other way around, respectively.

* bd_link/unlink_disk_holder() to create and remove holder/slave
  symlinks.

* open_by_devnum() wraps bdget() + blkdev_get().

The interface is a bit confusing and the decoupling of open and claim
makes it impossible to properly guarantee exclusive access as
in-kernel open + claim sequence can disturb the existing exclusive
open even before the block layer knows the current open if for another
exclusive access.  Reorganize the interface such that,

* blkdev_get() is extended to include exclusive access management.
  @holder argument is added and, if is @FMODE_EXCL specified, it will
  gain exclusive access atomically w.r.t. other exclusive accesses.

* blkdev_put() is similarly extended.  It now takes @mode argument and
  if @FMODE_EXCL is set, it releases an exclusive access.  Also, when
  the last exclusive claim is released, the holder/slave symlinks are
  removed automatically.

* bd_claim/release() and close_bdev_exclusive() are no longer
  necessary and either made static or removed.

* bd_link_disk_holder() remains the same but bd_unlink_disk_holder()
  is no longer necessary and removed.

* open_bdev_exclusive() becomes a simple wrapper around lookup_bdev()
  and blkdev_get().  It also has an unexpected extra bdev_read_only()
  test which probably should be moved into blkdev_get().

* open_by_devnum() is modified to take @holder argument and pass it to
  blkdev_get().

Most of bdev open/close operations are unified into blkdev_get/put()
and most exclusive accesses are tested atomically at the open time (as
it should).  This cleans up code and removes some, both valid and
invalid, but unnecessary all the same, corner cases.

open_bdev_exclusive() and open_by_devnum() can use further cleanup -
rename to blkdev_get_by_path() and blkdev_get_by_devt() and drop
special features.  Well, let's leave them for another day.

Most conversions are straight-forward.  drbd conversion is a bit more
involved as there was some reordering, but the logic should stay the
same.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Neil Brown <neilb@suse.de>
Acked-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Philipp Reisner <philipp.reisner@linbit.com>
Cc: Peter Osterlund <petero2@telia.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <joel.becker@oracle.com>
Cc: Alex Elder <aelder@sgi.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: dm-devel@redhat.com
Cc: drbd-dev@lists.linbit.com
Cc: Leo Chen <leochen@broadcom.com>
Cc: Scott Branden <sbranden@broadcom.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Cc: Joern Engel <joern@logfs.org>
Cc: reiserfs-devel@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
2010-11-13 11:55:17 +01:00

355 lines
7.9 KiB
C

/*
* linux/drivers/char/raw.c
*
* Front-end raw character devices. These can be bound to any block
* devices to provide genuine Unix raw character device semantics.
*
* We reserve minor number 0 for a control interface. ioctl()s on this
* device are used to bind the other minor numbers to block devices.
*/
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/major.h>
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/raw.h>
#include <linux/capability.h>
#include <linux/uio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/mutex.h>
#include <linux/gfp.h>
#include <linux/compat.h>
#include <asm/uaccess.h>
struct raw_device_data {
struct block_device *binding;
int inuse;
};
static struct class *raw_class;
static struct raw_device_data raw_devices[MAX_RAW_MINORS];
static DEFINE_MUTEX(raw_mutex);
static const struct file_operations raw_ctl_fops; /* forward declaration */
/*
* Open/close code for raw IO.
*
* We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
* point at the blockdev's address_space and set the file handle to use
* O_DIRECT.
*
* Set the device's soft blocksize to the minimum possible. This gives the
* finest possible alignment and has no adverse impact on performance.
*/
static int raw_open(struct inode *inode, struct file *filp)
{
const int minor = iminor(inode);
struct block_device *bdev;
int err;
if (minor == 0) { /* It is the control device */
filp->f_op = &raw_ctl_fops;
return 0;
}
mutex_lock(&raw_mutex);
/*
* All we need to do on open is check that the device is bound.
*/
bdev = raw_devices[minor].binding;
err = -ENODEV;
if (!bdev)
goto out;
igrab(bdev->bd_inode);
err = blkdev_get(bdev, filp->f_mode | FMODE_EXCL, raw_open);
if (err)
goto out;
err = set_blocksize(bdev, bdev_logical_block_size(bdev));
if (err)
goto out1;
filp->f_flags |= O_DIRECT;
filp->f_mapping = bdev->bd_inode->i_mapping;
if (++raw_devices[minor].inuse == 1)
filp->f_path.dentry->d_inode->i_mapping =
bdev->bd_inode->i_mapping;
filp->private_data = bdev;
mutex_unlock(&raw_mutex);
return 0;
out1:
blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
out:
mutex_unlock(&raw_mutex);
return err;
}
/*
* When the final fd which refers to this character-special node is closed, we
* make its ->mapping point back at its own i_data.
*/
static int raw_release(struct inode *inode, struct file *filp)
{
const int minor= iminor(inode);
struct block_device *bdev;
mutex_lock(&raw_mutex);
bdev = raw_devices[minor].binding;
if (--raw_devices[minor].inuse == 0) {
/* Here inode->i_mapping == bdev->bd_inode->i_mapping */
inode->i_mapping = &inode->i_data;
inode->i_mapping->backing_dev_info = &default_backing_dev_info;
}
mutex_unlock(&raw_mutex);
blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
return 0;
}
/*
* Forward ioctls to the underlying block device.
*/
static long
raw_ioctl(struct file *filp, unsigned int command, unsigned long arg)
{
struct block_device *bdev = filp->private_data;
return blkdev_ioctl(bdev, 0, command, arg);
}
static int bind_set(int number, u64 major, u64 minor)
{
dev_t dev = MKDEV(major, minor);
struct raw_device_data *rawdev;
int err = 0;
if (number <= 0 || number >= MAX_RAW_MINORS)
return -EINVAL;
if (MAJOR(dev) != major || MINOR(dev) != minor)
return -EINVAL;
rawdev = &raw_devices[number];
/*
* This is like making block devices, so demand the
* same capability
*/
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
/*
* For now, we don't need to check that the underlying
* block device is present or not: we can do that when
* the raw device is opened. Just check that the
* major/minor numbers make sense.
*/
if (MAJOR(dev) == 0 && dev != 0)
return -EINVAL;
mutex_lock(&raw_mutex);
if (rawdev->inuse) {
mutex_unlock(&raw_mutex);
return -EBUSY;
}
if (rawdev->binding) {
bdput(rawdev->binding);
module_put(THIS_MODULE);
}
if (!dev) {
/* unbind */
rawdev->binding = NULL;
device_destroy(raw_class, MKDEV(RAW_MAJOR, number));
} else {
rawdev->binding = bdget(dev);
if (rawdev->binding == NULL) {
err = -ENOMEM;
} else {
dev_t raw = MKDEV(RAW_MAJOR, number);
__module_get(THIS_MODULE);
device_destroy(raw_class, raw);
device_create(raw_class, NULL, raw, NULL,
"raw%d", number);
}
}
mutex_unlock(&raw_mutex);
return err;
}
static int bind_get(int number, dev_t *dev)
{
struct raw_device_data *rawdev;
struct block_device *bdev;
if (number <= 0 || number >= MAX_RAW_MINORS)
return -EINVAL;
rawdev = &raw_devices[number];
mutex_lock(&raw_mutex);
bdev = rawdev->binding;
*dev = bdev ? bdev->bd_dev : 0;
mutex_unlock(&raw_mutex);
return 0;
}
/*
* Deal with ioctls against the raw-device control interface, to bind
* and unbind other raw devices.
*/
static long raw_ctl_ioctl(struct file *filp, unsigned int command,
unsigned long arg)
{
struct raw_config_request rq;
dev_t dev;
int err;
switch (command) {
case RAW_SETBIND:
if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
return -EFAULT;
return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
case RAW_GETBIND:
if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
return -EFAULT;
err = bind_get(rq.raw_minor, &dev);
if (err)
return err;
rq.block_major = MAJOR(dev);
rq.block_minor = MINOR(dev);
if (copy_to_user((void __user *)arg, &rq, sizeof(rq)))
return -EFAULT;
return 0;
}
return -EINVAL;
}
#ifdef CONFIG_COMPAT
struct raw32_config_request {
compat_int_t raw_minor;
compat_u64 block_major;
compat_u64 block_minor;
};
static long raw_ctl_compat_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct raw32_config_request __user *user_req = compat_ptr(arg);
struct raw32_config_request rq;
dev_t dev;
int err = 0;
switch (cmd) {
case RAW_SETBIND:
if (copy_from_user(&rq, user_req, sizeof(rq)))
return -EFAULT;
return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
case RAW_GETBIND:
if (copy_from_user(&rq, user_req, sizeof(rq)))
return -EFAULT;
err = bind_get(rq.raw_minor, &dev);
if (err)
return err;
rq.block_major = MAJOR(dev);
rq.block_minor = MINOR(dev);
if (copy_to_user(user_req, &rq, sizeof(rq)))
return -EFAULT;
return 0;
}
return -EINVAL;
}
#endif
static const struct file_operations raw_fops = {
.read = do_sync_read,
.aio_read = generic_file_aio_read,
.write = do_sync_write,
.aio_write = blkdev_aio_write,
.fsync = blkdev_fsync,
.open = raw_open,
.release = raw_release,
.unlocked_ioctl = raw_ioctl,
.llseek = default_llseek,
.owner = THIS_MODULE,
};
static const struct file_operations raw_ctl_fops = {
.unlocked_ioctl = raw_ctl_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = raw_ctl_compat_ioctl,
#endif
.open = raw_open,
.owner = THIS_MODULE,
.llseek = noop_llseek,
};
static struct cdev raw_cdev;
static char *raw_devnode(struct device *dev, mode_t *mode)
{
return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
}
static int __init raw_init(void)
{
dev_t dev = MKDEV(RAW_MAJOR, 0);
int ret;
ret = register_chrdev_region(dev, MAX_RAW_MINORS, "raw");
if (ret)
goto error;
cdev_init(&raw_cdev, &raw_fops);
ret = cdev_add(&raw_cdev, dev, MAX_RAW_MINORS);
if (ret) {
kobject_put(&raw_cdev.kobj);
goto error_region;
}
raw_class = class_create(THIS_MODULE, "raw");
if (IS_ERR(raw_class)) {
printk(KERN_ERR "Error creating raw class.\n");
cdev_del(&raw_cdev);
ret = PTR_ERR(raw_class);
goto error_region;
}
raw_class->devnode = raw_devnode;
device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
return 0;
error_region:
unregister_chrdev_region(dev, MAX_RAW_MINORS);
error:
return ret;
}
static void __exit raw_exit(void)
{
device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
class_destroy(raw_class);
cdev_del(&raw_cdev);
unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), MAX_RAW_MINORS);
}
module_init(raw_init);
module_exit(raw_exit);
MODULE_LICENSE("GPL");